Culturing of lactic acid bacteria has been conducted in various manners, and is most often carried out by using animal milk as a culture medium for production of lactic acid bacteria formulations or production of fermented milk, lactic acid bacteria beverages, cheese and the like. However, since, in general, nutritional requirements of lactic acid bacteria vary among species, some lactic acid bacteria may not sufficiently grow in a culture medium consisting only of animal milk. Further, even when bacterial strains exhibiting a relatively higher proliferation activity are used in such a culture medium consisting only of animal milk, it is required to carry out culturing of the bacteria for several days in order to obtain fermented products having a sufficient acid level in producing fermented milk, lactic acid bacteria beverages and the like.
However, since culturing of lactic acid bacteria over a long period of time causes a reduction in the viable cell count, such a culturing technique is not always considered as a favorable culturing method for production of lactic acid bacteria beverages, fermented milk and the like for which various physiological effects are expected and for which viable cell counts are considered important.
Furthermore, for production of various beverages or foods in which flavors of fermented products obtained by culturing lactic acid bacteria are considered critical, bacterial strains used therein cannot be selected only from a viewpoint of their proliferative capacities. Consequently, there are cases where lactic acid bacteria providing fermented products having good tastes are selected and used, even if their proliferative capacities are inferior.
Therefore, in culturing of lactic acid bacteria, it is an ordinary technique that various growth-promoting substances are preliminary added to culture media in order to improve the culturing efficiencies, and such a technique has been well-known. In general, as examples of those which have been considered effective as growth-promoting substances, chlorella extracts, iron salts, vitamins, protein digests containing amino acids or peptides, yeast extracts, and the like can be mentioned.
The present Applicant has also reported that an extract of Rubus suavissimus S. Lee (Rosaceae) or the like are added to culture media in order to enhance the proliferative capabilities or survivability in culturing of lactic acid bacteria Patent Document 1.
However, in products such as fermented milk in which an extract of Rubus suavissimus S. Lee (Rosaceae) has been added, while the proliferative capability or survivability of lactic acid bacteria could be enhanced, the products had bitterness which is derived from the Rubus suavissimus S. Lee (Rosaceae), and therefore, had a problem in their tastes.